Sound signal



Nov. 21, 1933 R. M. CRITCHFIELD SOUND S IGNAL Filed April l8, 1927 Fig.1 W 777 6% 6R0: new

Patented Nov. 21, 1933 SOUND SIGNAL,

Robert M. Critchfield, AndersonQ Ind assignor to Delco-Remy Corporation, Dayton, Ohio, a corporation of Delaware Application April "18, 1927. serial no. 184,509 ;8 Claims. (01. iii-7i This invention relates to sound signals for automotive vehicles and one of its objects is to produce a signal which is penetrating in quality and produces a distinctive low tone so that it will be readily 'distinguishable from present typesof warning signals. a One of the contemplated uses of the present invention is for automobile passenger busses, and it is intended that the signal shall be sounded by the driver upon arriving at a waiting room for passengers in order to notify them of the arrival of the conveyance. By reason'of its distinctive low but penetrating note the passengers can readily distinguish the signal from the higher pitched signals ordinarily used by'pleasure vehicles. 7

'In one form of the present invention, the objects thereof are accomplished by a structure comprising a plurality of diaphragms operating simultaneously at different frequencies inseparate sound chambers communicating witha single projector. When the diaphragms are-operated at different frequencies, sound interference beats will be produced. "The-frequencies of the diaphragms may be such that the frequency of the beat is about 100 per second, thereby producing a guttural, distinctive tone of low pitch. While this tone may be mixed with tones of 'a higher pitch produced by the diaphragms separately, the tone produced by the beats willpredominate. l r

Further objects and advantagesof the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of embodiment of the present invention is clearly shown. 9

In the drawing: Fig. 1 is a side elevation partly inlongitudinal section of a form of the present invention." Figs. 2, 3 and 4 are sectional views taken respectively on the lines 2+2, 3-3 and 4-4 of Fig. 1.

Referring to the drawing, the signal comprises a frame 20 providing two or more throats 21 and 22 merging into a common outlet 23 which is connected with a projector 24. Each of the throats leads from a sound chamber 25, one .wall of which is provided by a flexible diaphragm 26 which is secured by screws 27 and a ring 28 to the flange 29 of a frame 30. Frame 30 may support any suitable magnet motor for operating the diaphragms. The one chosen for the purpose of illustration is a magnetmotor of theelectromagnetic type and includes an electromagnet coil 31 cooperating with an armature 32 and an E-shaped core '33. The armature is connected as shown with the diaphragm 26 and a tone-producing disc or vibratory body 34, and with a leaf spring 35 and a U-shaped member 36 carrying a screw 37 en gageable with a non-conducting button 38 attached to a leaf spring 39. Spring '39 carries a contact 40 engageable with a contact-'41. Contacts 40 and '41 constitute the circuit-make-and-break device in the circuit of the magnet coil 31. The function of the tone-producing disc 34 is to produce a tone of its own which is somewhat harmonious with the tone of the diaphragm 26 but is of higher frequency so that the combined tone of the diaphragm and disc is onein which a tone of medium pitch predominates but in which a clear ringing sound of higher pitch is clearly audible. When the mag net coil 31 is connected with a current source the armature 32 will be attracted toward the core33 to effect movement of the diaphragm in one direction and the separation of the contacts 40 and 41. The diaphragm 26 and the spring 35 urge the armature 32 away from the core to close the contacts 40, 41. This cycle of operations and the resulting vibration of the diaphragm 26 and disc 34 continues so long as the coil 31 is connected with a current source.

The diaphragm and magnet motor assembly which may, be designated in its entirety by numeral 50 is securedby screws 51 to a flange 52 of the frame, 20. In similar fashion a power plant 500. is secured to a flange 52a adjacent a sound chamber similar to the chamber 25 and in communication with the throat 21. The frequencies of the diaphragms of the magnet motor 50 and 50a differ in such manner that a sound interference beat of relatively low frequency will be produced. To this beat tone is added the higher pitched tones of the separate diaphragms and the still higher ringing tones produced by the separate tone-producing discs. The combination of tones produces one which is audibly distinct from the sound produced by warning signals usually employed on pleasure vehicles. In this way there has been produced a warning signal which is particularly adapted for passenger bus service. The passengers can be called from their waiting room by sounding the signal so that the driver will not need to leave the vehicle in order to call the passengers before departing.

In order that the diaphragm and magnet motor units will not interfere with each other during the operation. of both simultaneously, the wall 60 which separates the throats 21 and 22 should be of such length that the sound waves will not merge until after they have been pro-, jected a substantial distance from the diaphragms. It will be noted also that owing to the shape of the throats 21 and 22, the waves projected through these throats will enter the projector in substantially parallel paths. This arrangement is also believed to be desirable in order to prevent one diaphragm interfering with the other; 7 n

It is intended that the magnet motor 50a shall produce diaphragm vibrations of lower frequency than those produced by magnet motor" 50. The throat 22 is therefore longer than throat.

vibrated. The cross sectional area of the throats may be the same adjacent the sound'chambers but will increase uniformly in the direction of the projector. Hence area of the outlet of throat 22 is greater than thearea of the outlet of throat 21. as shown in Figs, 1 and l... The different lengths of the throats, and differing cross-sectional areas thereof areeach relatively characteristic of the associated magnet motors. ,In determining the charactenistics and dimensions, it is desirable to follow thesame formula-with respect to each unit 50 or 50a, and associated throat piece 21 and 22, sothat any local influence or mechanical interference will-be no more prominent in thetone productof one unitthan the other. When that practice is followed, the throat lengths and cross-sections will be designed to give the desired results of the tone elements in the respective chambers. That is,, the throat 22 being longer and of greater cross-section will be characteristic of the low pitch notes of the motor 50a while the throat 21 being shorter and of less cross-section will be characteristic of 'the high notes of the motor. 50. members 21 and 22 being of different length and cross-sections help to define resonating air columns for the magnet motors 50 and 50a, and of which each contributeto the tonal characteristics of their respectively associated magnet motors. The effective length of the vibrating air. column foreach magnet motor is therefore proportioned to it, and the effective cross-sectional area there'- of is changed, which produces a finaltone product of the instant desirability.

It will be understood without means of a wiring diagram that'th'e'i-magnet motors are connected simultaneously. with acurrent source by a switch so that'the diaphragms will vibrate simultaneously,z j 1 While'the form of embodiment .of-thepresent invention as herein disclosed, constitutes aspre ferred form, it is to be understood thatother forms might be adoptechall coming within scope of the claims which follow. I 1

What is claimed is as follows: U 1. A sound signal comprising a plurality of sound chambers, a single. projector, separate throats of difierent lengths each for connecting a sound chamber withtheprojector, adiaphragm in each sound chamber, means for vibrating'the the diaphragm at a frequency correspondingto the resonant frequency of the air column defined by the respective throat'andthe projector, said diaphragms being'actuated by their respective vibrating means and each at a diilerent frequency so as to produce a dissonance accompanied by sound interference beats when operating simultaneously. I a I v 2. In a sound signal the combination of a plu-' rality of sound emitting devices of different tonal characteristics, a projector, throats of.v different length andfuniformly increasing cross section each connecting a soun'd'emitting devicev with Therefore, the throatillustration by the projector, each of said sound emitting devices comprising a sound chamber, a diaphragm in each. of said chambers, a vibratory body and means for vibrating each of the diaphragms at a diiferent frequency, said devices being associated with the respective throat members to produce a dissonance imposed upon sound interference beats when the said sound emitting devices are operated simultaneously.

3;, A sound signal comprising a frame providingfa plurality of sound chambers and throats of different length and uniformly increasing cross section each throat connecting a sound chamber with=an outlet passage of the frame, a projector connected with said outlet passage, said throats directing the soundwaves emitting from the respective sound chambers to enter the projector in substantially parallel paths, means conveying the sound waves therealong a short distance before merging with each other, and a plurality of magnet motor and diaphragm assembly units attached to the frame, each comprising a diaphragm and means for vibrating the diaphragms at frequencies corresponding to the resonant frequencies of the air columns defined by the respective throats and the projector to which the throats are connected, and each diaphragm closing one of the sound chambers.

. 4., A sound signal comprising in combination,

a; projector, a branched throat member secured to said projector and having separate throat passages of different lengths and united to open in saidprojector, a magnet motor and sound pro ducing means mounted at the terminal of each branch of said throat member and vibrating at ,1

a frequency corresponding to the resonant frequency of the air column defined by the throat on which it is mounted and the projector, whereby. said {sound signalv will provide a pro'ector common to a pairof vibrating air columns difrespective units and merging into the'projector 1 as acommon conduit to form a branched air column having branches of different length and resonant to their respective sound producing units, whereby the effective length of the air column of each sound'producing unit will be characteristic of'the frequencies of the respective unit and individually contribute to produce a sounding signal of dissonance accompanied by sound interference beats when said units'are operating simultaneously.

6. In a sound signal, the combination comprising, a plurality of sound'producing units, a plurality of throats of different lengths connected with a common projector, said throats having a portion terminating in said projector and parallelto'each other at the outlets; and diaphragms respectively closing the other end of said throats, said diaphragms being vibrated by said sound producing units at frequencies corresponding to the resonant'lengths of the air columns provided by the. respective, throats and the projector to produce a sounding signal when said units are operating simultaneously.

ROBERT M. CRITCHFIELD. 

